It has already been proposed to use such rolls with a deformable casing as back-up rolls in mill stands, for example of the four-high type, for the rolling of flat products. These rolls make it possible, for example, to carry out corrections of thickness and planeness on the flat product during rolling.
The elements for holding the tubular casing in the radial direction relative to the fixed support generally consist of jacks, the chamber of which is machined in or attached to the fixed support, and the rod of which has, at its end facing the inner surface of the casing, a sliding outer surface providing a space making it possible to form a film of fluid between the block and the tubular casing. The casing, during its rotation, can thus slide on the end of the element virtually without friction.
In conventional rolls with a deformable casing, the same pressurized fluid feeds the chamber of the jack and the chamber of the block in order to form the sliding fluid film. These two chambers are therefore in communication with one another via a duct in the rod of the jack.
The feed pressure of the chamber of the jack must to be adjusted and modulated according to the adjustment parameters of the mill stand. A hydraulic feed circuit possessing hydraulic or electro-hydraulic adjustment elements must therefore be provided. Such elements are limited to a pressure of at most 300 bars in their operating state.
As regards a mill used for the processing of products requiring high rolling forces, this feed pressure of the jacks may prove inadequate, with the result that, in some phases of the rolling process, the rods of the jacks may be brought up against the fixed support in their chamber, although this is not too serious because, momentarily, it simply becomes impossible to adjust the stand, but above all the fluid film between the element and the tubular casing may be flattened completely, thereby causing destructive friction between the tubular casing and the element or even the fixed support.
In more general terms, where the rolling of any flat product is concerned, momentary excess pressures can arise, especially at the instant when the strip enters the mill stand. If the pressure of the fluid film between the holding elements and the tubular casing itself is insufficient, it can happen that the casing, holding elements and fixed support may be brought in contact with one another and are subjected to wearing or destructive friction.